Electromagnetic relay

ABSTRACT

An electromagnetic relay of the miniature relay type with a contact spring group and a magnetic circuit which comprises a substantially rectangular loop formed by a magnetic core and a magnetizing coil surrounding a part of the core. The core part surrounded by the coil is the armature of the relay, the armature being pivoted at one end and movable in a direction transversally to the axial direction of the coil and to the longitudinal direction of the armature.

United States Patent J ambrink et al.

ELECTROMAGNETIC RELAY Inventors: Karl Evert Jambrink, Grumsgatan 3,Farsta; Per Harry Elias Claesson,

Osterhagens Gard, Drevviken; Roll Albln Zander, Storhagsvagen 28'A,Alvsjn, all of Sweden Filed: Aug. 26, 1970 Appl. No.: 67,287

' Related US. Application Data Continuation of Ser. No. 723,451, Apr.23, 1968,

abandoned.

Foreign Application Priority Data I May 3, 1967 Sweden "62 81/67 Jan.31, 1968 Sweden .1251/68 us. c|...'. .335/135, 335/276 Int. Cl. ..no1n50/26 F1eldofSearch.. .335/135, 128, 124,187,203,

[451 Jan. 18, 1972 References Cited UNITED STATES PATENTS 2,692,31410/1954 Lawrence ..335/129 3,260,818 7/1966 Fisher et al. ..335/2743,431,521 3/1969 Kusano .....335/124 Primary Examiner-Harold BroomeAttorney-Strauch, Nolan, Neale, Nies & Kurz [57] ABSTRACT Anelectromagnetic relay of the miniature relay type with a contact springgroup and a magnetic circuit which comprises a substantially rectangularloop formed by a magnetic core and a magnetizing coil surrounding a partof the core. The core.

part surrounded by the coil is the armature of the relay, the armaturebeing pivoted at one end and movable in a direction transversally to theaxial direction of the coil and to the 1ongitudinal direction of thearmature.

' 21 Claims, 17 DrawingFigures PATENTED M18197? 3,636,483

SHEET 1 BF 4 INVENTORS KARL EVERT JARNBRINK BYPER HARRY ELIAS CLAESSONROLF ALBIN ZANDER PATENTEQ .mn 81972 3.838.483

sum 2 OF 4 /5 &

s a F79. 7 3 :5 1 I m 1/ y 1 '51 E INVENTORS KARL svsm .mmenmx PERHARR'Y ELIAS CLAESSON ROLF ALBIN ZANDER ATTORNEYS PATENTEDJANISIWZ3.636.483

SHEET 3 OF 4 KARL EVERT JARNBRINK HYPER HARRY ELIAS CLAESSON ROLF ALBINZANDER ATTORNEYS PATENTEUJANTSIQTZ asset-483 saw u or 4 Fly. /7

INVENTORS KARL EVERT JARNBRINK BYPER HARRY ELIAS CLAESSON ROLF ALBINZANDER JMWM m ATTORNEYS 23, 1968, now abandoned.

' LE TR MAG ETI RE AY This is a continuation of application No. 723

,451 filed Apr.

The present invention relates to an electromagnetic relay of very smalldimensions.

More specifically, the invention relates to an electromagnetic relaywhich has one or more contact spring groups, a magnetic circuit and acoil surrounding a part of the magnetic circuit. The magnetic circuitcomprises a ferromagnetic core which has the shape of a substantiallyrectangular loop. One side of the loop constitutes a movable armatureand is pivoted by one end thereof to the adjacent end of the rest of theloop, whichforrns the stationary part of the core. The other end of themovable armature forms a working airgap with the other end of thestationarycore part.

Further, there is anactuating rib in mechanical engagement with thearmature near the working alrgap. The actuatingrib is arranged totransmit movement from the armature to the movable contact spring orsprings of the contactspring group or groups.

.SUMIMARY or THEIINVENTION A primary object of theinvention resides inthe provision of a novel electromagnetic relay withsmall dimensions andhigh degree of reliability. I I A further object of the inventionresides in the provision of a novel small relay, the magnetic circuit ofwhich exerts a great traction force to the armature, in spite of thesmall dimensions, while maintaining the current consumption at a smallvalue, so that the heating of the relay coil will not exceed allowablelimits. A t

The invention, according to one aspect thereof, is substantiallycharacterized by the fact, that the relay armature is SUI? rounded bythe core with an airgap between the inner walls of the coil andat leastone side of the armature and that the armature is movable in the coiltransversally to the longitudinal axis thereof and that the stationarycore part is fixed relatively to the coil and adapted to substantiallyclose the magnetic circuitat one single side of the coil. I According toanother aspect of the invention, if the available area for the windingofthe coil inside the loop formed by the magneticcircuit is A and thewidth of the core part inside the coil is B, andits thickness is T,.thefollowing dimensional relations should be fulfilled:

' B-T/A 0.l I T/B 0.2 By such dimensioning arather distinguished maximumof the pulling force for a given volume of the relay and a given powerdissipation is surprisingly obtained. I In order to obtain suchoptimal'function, it is also suitable to I 8 ows .a side view ofa, el y.partly i sec iom or ing to a modified form of the present invention. I

FIG. 9 shows a front end view of therelay according to FIG. 8,

FIG. 10 is a top view of the same relay, FIG. 11 is a top view ofan-armature assembly used in any of the relays according to FIGS! to 3.and '4 to 6,

FIG. 12 is a side view of the samearma'ture assembly,

FIG. 13 is a top view of a pole sheet forming an airgap spacer comprisedin the armature assembly according to FIGS. 11 and 12, I

FIG. .1 4 is a side view of? contact spring group intended for any ofthe relays according to FIGS! to 3, FIGS.'4 to'6 or FIGS. 8 to 10, I

FIG. 15 is a front end view of the contact spring group according'toFIG. 14,

FIG. 16 is a side view of anothercontact spring group intended for thesame relays, and I FIG. 17 is a curve showing the traction force ofthearmature as a function of certain specific dimensions of a relayaccording to any of the Figures. I I v In FIGS. 1 to 3 there isillustrated anelectromagnetic relay I relating to the kind of relayscalled miniature relays. The relay is mounted on a bracket 1 which ismade from plastic or similar material. The bracket 1 is designed toserve as a support for a contact spring group 4 and also to serve as asupport design the magnetic coil so that when the nominal actuating.voltage is impressed to its terminal, the maximum allowable powershould be dissipated in thecoil in consideration of the allowableheating of the coil.

Further, the present invention relates to means and methods forassembling a relay of the type referred to and to contactspring groupsand actuating ribs for such relays.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 6 is a top view of one of thecontact spring groups used I in'the relay according to FIG. 4, I

FIG. 7 illustrates a part of the relay according to FIGS. 4 to 6 duringone stage of its asembling,

for and be integral with a coil bobbin of a magnetizing coil 2.

I The relay comprises also a magnetic circuit consisting of two parts 3,7. One of said parts 3, which is the stationary core part, is rigidlyconnected to that part of the bracket 1 which is integral with the coilbobbin. The other of said magnetic circuit parts, which is the movablepart or the armature 7, is by one end 74 thereof in contact'with one end3a of the fixed part 3 while the other end 7b of said movable part orarmature is so located, that a working airgap 1 6,is formed between theother end 3b of the fixed part 3. and said other end 7b of the movablepart 7. K It is apparent from] FIG. 1, that the armature 7 is movabletransversally within the aperture-in 'the magnetizing coil 2 and thatthe stationary magnetic core part 3forms a substantially closed magneticloop with the armature 7. Said magnetic loop is closed at one side onlyof the'magnetizing coil 2.

A contact spring group-4 is rigidly mounted on the stationary core part3 by means of a screw 5.0. The contact springs comprised in said contactspring group 4 have rear ends 4a which are intendedto be connected to anexternal circuit e.g., a printed circuit) by, for example, soldering.Said ends extend through apertures in an upstanding part vlb integralwith the bracket 1.

The front ends (not shown) of the movable contact springs in saidcontact spring group 4 are actuated by an actuating rib 107 the lowerend of which is in engagement with the armature 7 in order to transmitmovement from the armature 7 to said contact springs.

The upper end 1074 of the actuating rib 107 penetrates through anaperture in an upper plate 412. and is guided in said The rear end 3a ofthe stationary magnetic core part 3 is received in a pocket in thebracket 1. The front end 3b of said core part 3 is fastenedto the frontflange 2f of the bobbin for the magnetizing coil 2 by means of a screw 111.

The lower end of the actuating rib 107 has two legs 1070 and 107d whichare guided in lateral recesses (not shown) in the front end 3b of thestationary core part 3.

In FIGS. 4 to 6 there is illustrated a second embodiment of theinvention, which is in all essential similar to the embodiment alreadydescribed. I

In a'coil bobbin belonging to the bracket 1 which has a rear flange 14and a front flange 12, a winding 2 is provided. A U- shaped stationaryiron core part 3 has rear and front legs 34 and 3b, respectively, andcarries two contact spring groups 4 which are fastened to said core partby means of screws 5. The

movable contact springs of said contact spring group are actuated by anactuating rib 107, which will be described more in detail later. I I IWhen the relay is assembled, (see FIG. 7), an opening 11 whichis-provided in the front leg 3b of said stationary core part 3 is forcedover a projection 13 provided on the front flange 12 of the coil bobbinbelonging to the bracket 1, and, thereafter, the rear leg 3a of saidcore part 3 is pushed down in a pocket behind the coil bobbin 2 and infront of an upstanding part 15 of said bracket I. Said projection 13should preferably be slightly conical in order to facilitate themounting, and, by this means, the core part 3 and the front wall of thebobbin 2 will be rigidly fastened to each other.

Alternatively, the projection 13 may be smaller than the aperture 11 inthe bridge 3. In this case the stationary core part 3 and the bobbin 1can be fixed to each other by melting the outermost end of theprojection 13 by a heat tool. Altematively, the projection can be fixedin the aperture by glueing. But before this fastening is made, a fixtureshould be pushed into the airgap 16 to accurately determine the size ofsaid airgap in a simple way.

As an alternative, it is, of course, possible to provide an aperture inthe flange 12 of the bobbin and a corresponding projection on the leg 3bof the core part 3, if this should be preferred for some reason.

Inside the coil 2, the armature 7 is movably located. The armature 7 isprovided with a fastening spring 8 which, when the armature is pushedinto the bobbin, engages the front leg 3b of the stationary core part 3and thus locks the armature within the bobbin, so that the armature isprevented from sliding out of the bobbin in an opposite direction to thedirection, in which it was pushed in. The armature is prevented fromsliding out from the bobbin in the other direction by the upstandingpart 15 of said bracket 1. The rear end of the armature 7 is in contactwith the rear leg 3b of the stationary iron core part 3. The distancebetween the front end of the armature 7 and the end of the front end 3aof the core part 3 forms the working airgap 16. When the armature is inits unactuated or rest posi-' tion, its location is determined by thebottom surface of said armature 7. As illustrated, said surface rests onthe inner wall surface of the coil bobbin.

When the armature 7 is actuated or, after actuation, is restored to itsrest position, there will be, during the movement of the armature, anair cushion which is compressed within a limited volume between thearmature and the walls of the coil bobbin. This air cushion is highlydamping the movement of the armature and prevents the armature frombouncing when it reaches any of its end positions, and by such bouncingto inadvertently actuate the springs in the contact spring group. Thisdamping is very effective, especially if the width of the armature isonly slightly less than the width of the opening in the coil bobbin.

It has been mentioned in the foregoing, and it will be obvious from FIG.4, that the location of the armature 7 in its rest position isdetermined by a wall in the coil bobbin. Further, said coil bobbin,according to the foregoing, is fastened to the stationary core part 3.Therefore, the size of the working airgap l6 will be accuratelydetermined.

The stationary core part 3 and its rear leg 3a will be fixed to the coilbobbin by the contact spring group 4, because said contact spring groupwill be fixed relative to the bracket 1 by means of the connection endsof the contact springs which penetrate apertures in the upstanding part15 of said bracket 1.

The mounting of the contact spring group in this embodiment of the relayis carried out in the following way.

First, the contact spring group is pushed backwards as far as possibleon the relay whereby the connection ends of the contact springspenetrate the apertures in the upstanding part 15 of the bracket 1 ofthe relay. Thereafter, the actuating rib 107 is put into place betweenthe front leg 3b of the stationary core part 3 and the front flange 12of the coil bobbin. When the contact spring group 4 thereafter is pushedforwards, to its final position, the movable contact springs willpenetrate the actuating rib 107 and will be moved to their correctpositions in relation to the different supporting surfaces of theactuating rib, which will be described more in detail in connection withthe description of the contact spring functions.

The actuating rib 107 has an upper portion which is bifurcated and hastwo upstanding projections l07b and 107C. Said legs are guided inrecesses 25a and 25b, respectively (FIG. 6) in a top plate 25 belongingto the contact spring group. At its bottom end, the actuating rib 107 isprovided with two legs 107d and 107f which project downwards between thefront end of the bobbin of the magnetic coil 2 and lateral projections30 and 3d of the front end 3b of the stationary core part 3. The bottomends of said legs 3c and 3d are in engagement with side projections 70and 7d, respectively of the armature 7, as will be apparent from FIGS. 4and 5. The lateral projections 3c and 3d of the stationary core part 3and the corresponding lateral projections 70 and 7d of the armature formpole-shoes which enlarge the magnetic surfaces between which the workingairgap is formed. As already stated, this allows for such dimensioningof the magnetic circuit, that other parts of the core and armature maybemagnetically saturated during normal use of the relay. This is anothercondition for obtaining maximum pulling force fora given size and agiven power dissipation.

In FIGS. 8 to 10 a modified embodiment of the invention is described.

According to this embodiment, the stationary iron core part 3 is locatedinside the coil bobbin for the magnetic coil 2 and the movable core partor the armature 7 is located outside the coil.

The stationary core part 3 is kept in place by the coil bobbin. Thearmature 7 is pivoted at its rear end 7a. It is inserted into a suitableopening 1d of the rear flange of the coilbobbin. It is forced into saidopening 1d in the somewhat elastic flange. There are two lateralrecesses (not shown) in said armature 7 in which the edges-defining theopening 1d are received after pushing in said armature. By this means,the armature is kept in place in its inserted position. I

At the front end of the relay, the armature 7 is guided andtransversally movable in an opening 1e in the front flange of said coilbobbin.

Both the stationary core part 3 and the armature 7 are L shaped andidentical to each other.

A contact spring group 4 is fastened to a sheet metal plate by a screwor rivet 101. Said plate 100 has a down-bent rear flap 102 which isreceived in a pocket in the bracket 1 and abuts against the rear, upperside of the stationary core part 3. Therefore, the position of thespring group 4 is always accurately defined relative to the magneticcircuit and independent of dimensional alterations in the insulationmaterial of the bracket 1. i

The plate 100 has bent-down side portions. The lowermost edges of saidside portions are bent inwards to be received in recesses in the frontwall of the front flange of the coil bobbin as shown at 100a and 10% inFIG. 9.

The contact spring group is actuated by an actuating rib 107 which is ofsimilar construction and functions similarly to the actuating rib 107 inFIGS. 1 to 3.

For facilitating the release of the relay while the residual magnetismin the magnetic circuit is still rather strong (which is necessary forobtaining a rapid releasing function) it is necessary to provide anonmagnetic pole-pin or pole-sheet in the working airgap between thearmature 7 and the stationary core part 3. i

The armature 7 with its side projections 70 and 7d and with a fasteningspring 8 and a pole sheet 21 attached to it, is illus trated in FIGS. 11and 12. The pole sheet 21 is illustrated separately in FIG. 13.

The fastening spring 8 is fastened to the armature 7 in the vicinity ofthe pivoting point, near the end 7a of said armature. This fastening canbe made by, for example, spot-welding. Said spring 8 is pretensioned sothat its free end near the working airgap is bent upwards. When thearmature is inserted into the relay, the end of said spring part 8 willbe in engagement with the inside of the front end 3a of the stationarypart 3, and thus lock the armature 7 in inserted position. Said free endof the spring 8 inside the coil bobbin is preferably broader than thearmature. By this means, the armature 7 will be locked against lateralmovements and the armature will be free from engagement with the innersides of the coil bobbin so that friction between the sides of thearmature and the adjacent parts of the coil bobbin will be avoided.

For fastening the pole-sheet 21 to the armature assembly illustrated inFIGS. 11 and 12, said pole-sheet is provided with a narrow middleportion 21a which is pushed into an opening 19 in the-fastening spring 8as illustrated. I

The relay according to FIGS. 4 to 6 has a contact spring group 4 whichis illustrated in detail in FIG. 4. Said contact spring group has threechangeover contacts which is apparent from FIG. 4. One of saidchangeover contacts comprises the contact springs 27, 28 and 29 and asupporting spring 30. The supporting spring as well as the contactspring 27 are rigid as compared to the springs 28 and 29. The contactspring 28 is bent towards the contact spring 27, so that the desiredcontact pressure is obtained. Further, the contact spring 29 is benttowards the supporting spring 30, so that, when the contact spring 28,through actuation by the part 31 of the actuating rib 107 is movedupwardly so as to lift the spring 29 from the spring 30, a desiredcontact pressure between the contact springs 28 and 29 will be obtained.The movement by spring action of the rigid contact springs 28 and 30should, of course, be small as compared to the movement of the springs28 near the part 31 of the contact rib 107 when the armature isactuated. Another changeover contact in the same contact spring groupcomprises the contact springs 37 to 40. This changeover contact isidentical to the just described changeover contact and, therefore, thischangeover contact need not be described more in detail here.

A third changeover contact in the same contact spring group comprisesone rigid spring 32,'one moveable contact spring 33 and one fixedcontactspring 34 and, in addition to that, one rigid supportingspring 35. Thischangeover contact isfunctioning in the same way as the just describedchangeover contacts. It will be apparent from FIG} 4, however, that therigid spring 32 is double bent to have the shape of a z, in

, the direction towards the movable spring 33 at the end 'where thecontacts are provided. Similarly, the fixed spring 34 is double bent inthe same way in the direction towards the spring 33, at the end wherethe contacts are provided. By this means, the heights of the solidcontact parts isconsiderably decreased as compared to the solid contactparts of the contact springs 27, 30 in the changeover contact previouslydescribed, and, therefore, the quantity of contact material in saidsolid contacts is considerably decreased. In case that a precious metalis used for the contacts, it is of course advantageous from aneconomical point of view, to need rather small quantities of materialfor the solid contacts. The quantity of material should be determined bythe quantity of material which is required because of the loss ofmaterial due to migration (contact erosion) and not by the distancebetween the contact springs, which is determined by the thickness of theinsulation spacing washers between the contact springs. The thickness ofsaid washers is, in turn, determined by the requirements of insulationbetween the contact springs.

In order to obtain good contacts, the changeover contact springs 28 33and 37 and the upper springs 29., 34 and 39 ought to be bifurcated sothat twin contacts are obtained in a manner known per se. In order toeliminate vibrations or contact bounces, when the contacts are closed orbroken, the shanks of the bifurcated portions should be taperingforwardly in a direction from the nonbifurcated portion towards thecontacts. Further, those parts of the actuating rib 6 which are engagingthe movable contact springs as well as the supporting points, where thesupporting springs 30, 35 and 40 cooperate with the associated contactsprings, ought to be as close to the contacts as possible. Therefore,said parts of the actuating rib towards the contacts, which will beapparent from FIG. 4.

As will be apparent from FIG. 5, which illustrates the relay as viewedfrom the rear end thereof, two contact spring groups may be mounted onthe core part 3. The contact spring groups are assembled in a mannerknown per se by means of insulating spacing washers between the springs.Each contact spring assembly is clamped together by means of a hollowrivet 4! (FIG. 6).

In FIGS. 14 and 15 there is illustrated a contact spring groupcomprising one break contact and one double make contact. The contactspring group comprises one rigid contact spring 46, one movable contactspring 47, two fixed contact springs 48 and 50 and two rigid supportingsprings 49 and 51.

Because the actuating rib 107 has the shape of a ladder, the

located more close to the clamping part of the spring. How the I contactspring group functions, when the part 45 of the actuating rib 107 isdisplaced by the armature, may be apparent from FIG. 14 without detailedexplanation.

The contact spring group according to FIG. 16 comprises one breakcontact and one continuous changeover contact. The contact spring groupcontains one rigid, fixed contact spring 46, one movable contact spring52, and, further, one rigid contact spring 53 and one bendable, fixedcontact spring 54.As in the embodiment according to FIG. 14, thecontacts belonging to one contact function (the make contact function ofthe continuous changeover contact) are located inside the contactactuating rib 107 in order to obtain great contact movements.

In order that the rigid springs, such as the springs 27 and 30 in FIG. 4should not be appreciably bent when they are loaded by the contactpressure, which would bring about contact bounces and improper contactfunctions, such rigid springs In order to'avoid contact bounces, themovable contact springsand the supported'fixed contact springs shouldhave a very low mass, i.e., they should be rather thin, so that themaximum bending stress exceeds 20 kgJmm. (2,-800 pounds per square'inch)and, as previously stated, the supporting surfaces and the actuatingsurfaces of the actuating rib should be adapted to cooperate with thecontact springs close to the contacts.

In known constructions of contact spring groups for relays of theminiature relay type, the fixed contact springs comprised in the'breakfunction of the changeover contact (cor responding to springs 27, 32 and37 in FIG. 4) have had the form of double springs, viz one rather softcontact spring and one rather rigid supporting spring. According to thepresent invention, only one rigid spring is required for the samepurpose which, of course, decreases the production costs for the relay.Similarly, the contacts which correspond to the spring 46 in FIG. 14 and46 and 53in FIG. 16 have usually comprised two springs each, butaccording to the present invention, such contacts have been simplifiedto comprise only one contact spring each.

By the dimensioning rule indicated in the foregoing, i.e., that theratio between the cross section area of the magnetic core and the areaof the opening for the magnetizing coil should exceed 0.1 and preferablybe between 0.2 and 1.0 and that the ratio of the thickness to the widthof the core part inside the magnetizing coil should be more than 0.2,the benefit would be obtained, among others, that a better cooling willbe achieved, provided that the compared relays have similar totaldimensions. In an ordinary relay of the L-shaped armature type, and witha length of 30 mm. a height of 30 mm. and a width of 19 mm., there wasobtained a temperature increase of 66 C. when the coil was supplied witha constant voltage, giving a dissipated power of 1.85 watts in the relaycoil at 20 C.

-ambient temperature. The ratio mentioned in the foregoing vertical axisindicates the effective power supplied to the magnetizing coil and theabscissa or horizontal axis indicates the ratio between the core areaand the area of the opening available for the cross section of thewinding of the magnetizing coil, located between the core parts 3 and 7.The curve indicates said ratio provided that the volume of the wholemagnetizing circuit is constant. Further the curve is valid for acertain, favorable value of the ratio of the thickness to the width ofthe rectangular core in the coil. This means, of course, that when thevolume of the parts 3 and 7 increases, there will be acorrespondingdecrease of the volume of the coil winding. The indicatedvalues of the vertical axis is in watts, i.e., the maximum effect isindicated to be about 1.5 watts. The curve is computed and tested forsuitable dimensions of the magnetic circuit of the relay where the coreparts 3 and 7 and the winding with the coil bobbin included has thefollowing dimensions: length 27 mm., width 17 mm. (the width of thecoil) and height 17 mm. For a value on the horizontal axis of 0.56 apulling force of 640 grams will be obtained, when the working airgap is0.18 mm. and the supplied efiective power is 0.64 watts. The pullingforce is 320 grams, when the airgap is 0.36 mm. and the effective poweris 0.85 watts. These values are calculated for a circuit without poleshoes. The dotted curve is calculated for the parts 3 and 7 beingprovided with pole shoes which extend substantially along the wholewidth of the outer flange of the coil bobbin. It is evident from thecurves, that a pronounced minimum point is obtained, when the ratiobetween the core area and the opening for the magnetizing winding isbetween 0.2 and 0.6 but it is also evident from the curve that saidratio ought to be greater than 0.1. Very acceptable values are obtainedeven if the ratio is allowed to vary between 0.1 to 2.0. l

It should, however, be emphasized that about three times as greatpulling force will be obtained under similar conditions by, saiddimensioning rule as compared to relays, which at present are availablein the market. It is obvious, however, that the curve shown in FIG. 17would be somewhat altered, if other fixed dimensions are used as basevalues. Thus, a still better optimal value will be obtained, if thelength of the circuit is somewhat greater.

It has been stated in the foregoing, that the stationary core part 3 andthe armature 7 should have substantially equal cross section areas. Inthis connection it should be mentioned that a certain leakage fieldalways is present around the coil and, therefore, the part which isenclosed in the coil has always a slightly greater magnetic field thanthe other part. The difference in field intensity in the case nowdiscussed is supposed to be ofthe order of 10 percent. This means, thatfor obtaining an optimal dimensioning, the part outside the coil shouldhave slightly greater cross section area than the part inside the coil.The expression substantially equal cross section area for these parts ismeant to include such minor differences between the areas of the twoparts.

It should be noted, that by making one of the parts U- shaped, thebenefit is obtained that the legs of such part can be groundsimultaneously for providing a good contacting surface against the otherpart with well defined dimensions. It should also be noted, that suchgrinding will not alter the pole surface area. i

It is a known fact that when the relay should be used in dustysurroundings, contact faults will easily occur if the dust has access tothe contacts. For avoiding such contact faults, attempts have been madeto cover the relays by suitable caps. But in this case there will be arisk for a so-called activating of the contacts, due to the vapors,especially carbon hydrogen vapors, which are generated by the insulationmaterial in the relay. According to this invention, both of thelast-named disadvantages are avoided by enclosing the relay by a cap, anenvelope or the like, which is provided with at least one opening inwhich a dust filter is inserted.

In FIG. 4, there is a cap 17 illustrated, preferably made from plastic,which is pushed over the relay from the front end thereof, i.e., the endwhere the contacts are located. At the other rear end of the relay,there is a backplate which is designated as a washer 18, preferably of aporous material, for example foam rubber or some other material, whichhas dustfiltering characteristics. Washer 18 has apertures for theconnection ends of the contact springs of the relays. The connectionends should hermetically penetrate the apertures, so that dust would notbe able to penetrate through the apertures. Washer 18 can be locatedinside or outside the upstanding part 15 of the bracket 1 which isintegral with the coil bobbin.

Alternatively, an air ventilation may be arranged at other locations inthe walls of the cap, for example in the neighborhood of the contacts.Thus, the cap 17 is shown to have one or more ventilation openings 17a,in which units 17b made from air filter material of a known type areinserted and fastened by means of, for example, glueing. Thelast-mentioned filter does not exclude the simultaneous use of otherfilters of the type described above at the rear end of the relay.

What is claimed and desired to be secured by Letters Patent is:

1. An electromagnetic relay comprising: at least one contact springgroup; a magnetic circuit; and a coil surrounding a part of saidmagnetic circuit; said magnetic circuit comprising a ferromagneticassembly which has the shape of a substantially rectangular loop, oneside of said loop constituting a movable armature; means mounting oneend of said armature in pivotal disposition to the adjacent end of astationary loop part constituted by the rest of said magnetic loop andproviding a working airgap between the other end of said armature andthe respective adjacent, other end of said stationary loop part; anactuating rib in mechanical engagement with the other end of saidarmature near said working airgap, said actuating rib being disposed totransmit movement from the armature to any movable contact spring of asaid associated contact spring group, said armature being disposedthrough said coil with an airgap between the inner walls of the coil andat least one side I of said armature, said armature being pivotablymovable in said coil transversally to the longitudinal axis thereof; andsaid stationary loop part being fixed relatively to said coil andadapted to substantially close the magnetic circuit at one single sideof said coil.

2. An electromagnetic device comprising: a stationary magnetic circuitpart; a magnetizing coil and a movable armature, characterized by thefact, that the stationary part is located wholly outside said coil andextends parallel to the axis of the coil from one end of the coil to theother, and that said movable armature is located inside said coil andbeing pivoted at one end adjacent to an end of said fixed stationarypart at one end of said coil; space within said coil enabling pivotalshift of said armature; and the other end of said armature disposedoutside the other end of said coil and forming a working airgap withsaid stationary part.

3. An electromagnetic device according to claim 2, characterized by thefact, that said stationary part is parallel to the coil axis and locatedonly at one side of said coil and that said armature is disposed so itssaid other end shifts to and from said stationary part and by suchmovement the size of the working airgap is decreased and increasedrespectively.

4. An electromagnetic relay device according to claim 2, characterizedby the fact that a coil bobbin is provided; at one side of said armaturea leaf spring is disposed within said coil, said spring having a freeend which abuts against the inside wall surface of said coil bobbin andkeeps said movable armature in such a position that a working airgap issituated 15. A relay according to claim 13, characterized by the fact,that said cover is provided by at least one aperture in the vicinity ofthe contacts, in which a dust filter is inserted.

16. A relay according to claim 1, said relay comprising: at least onechangeover contact, characterized by the fact that said changeovercontact comprises one movable contact terized by the fact that said leafspring is provided with an aperture, a strip of nonmetallic sheetmaterial is inserted through said aperture, one end of said stripextending to the airgap and forming a nonmetallic pole-sheet, forpreventing the pole surfaces from making direct contact with each other.

7. A relay according to claim 6, characterized by the fact that saidaperture in said leaf spring is elliptic and that said strip has aportion of reduced width adapted upon assembly to be located in saidaperture for fixing said strip in a predetermined, longitudinalposition. i

8. An electromagnetic device according to claim 2, characterized by thefact, that the cross-sectional areas of said fixed corepart and saidmovable armature have such dimensions that there will be magneticsaturation simultaneously in said core parts when normal actuationcurrent is passed through said coil that by such actuation a normalheating of said coil will occur within usual safety margins.

9. An electromagnetic device according to claim 3 charac-. terized by acoil bobbin, and the fact, that said stationary part is U-shaped, withthe legs thereof bent towards said movable armature, that cooperatinglug aperture means on a leg of said stationary part and said bobbininterlock said stationary core part to said coil bobbin.

10. A relay according to claim 1, comprising a coil bobbin for themagnetizing coil having a flange provided with an extension at one side,said extension enabling support for one end of contact springs belongingto said contact spring group.

.11. A relay according to claim 10, characterized by the fact, that saidextension has apertures therethrough, and circuit connection ends ofsaid contact springs penetrate through said extension apertures.

12. A relay according to claim 1, wherein the contact spring groups arecharacterized by the fact, that at least one contact set of the contactsprings is located in an aperture in said actuating rib.

13. An electromagnetic relay according to claim 1, comprising a coverfor said relay, characterized by the fact, that said cover is providedwith at least one opening in which a dust filter is inserted.

14. A relay according to claim 13, characterized by the fact, that saiddust filter comprises a porous washer located at the rear part of saidrelay, remote from the relay contacts, and that said filter is providedwith openings into which the exter nal connection parts of the springsare tightly fitted.

spring and one fixed contact spring and that said fixed contact springis considerably stiffer, by at least approximately ten times, than themovable spring, and that the contact means of said movable contactspring rests against the contact means of said fixed spring so that abreaking contact is obtained, and that said changeover contact furthercomprises a second fixed contact spring and a supporting spring, thesupporting spring supporting said second fixed spring and being at leastabout ten times stiffer than said second fixed contact spring thusproviding the make function of the changeover contact, and

finally that the supporting surface by which said supporting springsupports sat second fixedcontact spring and a so the surface of thatpartof the actuating rib which actuates the movable contact spring arelocated immediately adjacent to the contacts of said springs.

17. A relay according to claim 16, characterized by the fact,

that said fixed spring for the break function and said fixed spring forthe make function are double bentto have the shape of a z in thevicinity of the contacts thereof, towards the associated movable contactsprings, so that the height of the solid contacts of said springs isconsiderably less than the thickness of insulating spacing washerslocated between said contact springs.

18. An electromagnetic device comprising: a stationary magnetic circuitpart; a magnetizing coil and a movable armature; said stationary partbeing disposed outside said coil and extending parallel to the axis ofsaid coil from one end of said coil to the other end of said coil; saidmovable armature being disposed inside said coil; means pivoting saidmovable armature at one end adjacent to an end of said fixed stationarypart at one end of said coil, the space within said coil enablingpivotal shift of said armature; and the other end of said armature beingdisposed outside the other end of said coil and forming a working airgapwith said stationary part; the cross I section area of said armaturedivided by the area A of the space between the armature and thestationary part, available for the cross section of the winding of saidcoil, is greater than 0.1 and that the thickness of said armaturedivided by its width is greater than 0.2. I

19. An electromagnetic device as defined in claim 18, wherein thethickness T of the armature divided by its width B is greater than 0.35and preferably between 0.35 and 0.5.

20. An electromagnetic device as defined in claim 18,

wherein the cross section area of the armature divided by the area A ofthe space between the armature and the stationary part, available forcross section of thewinding of said coil, is greater than 0.2 andpreferably between 0.2 and 1.0.

21. An electromagnetic device as defined in claim 20, wherein thethickness T of the armature divided by its width B is greater than 0.35and preferably between 0.35 and 0.5.

1. An electromagnetic relay comprising: at least one contact springgroup; a magnetic circuit; and a coil surrounding a part of saidmagnetic circuit; said magnetic circuit comprising a ferromagneticassembly which has the shape of a substantially rectangular loop, oneside of said loop constituting a movable armature; means mounting oneend of said armature in pivotal disposition to the adjacent end of astationary loop part constituted by the rest of said magnetic loop andproviding a working airgap between the other end of said armature andthe respective adjacent, other end of said stationary loop part; anactuating rib in mechanical engagement with the other end of saidarmature near said working airgap, said actuating rib being disposed totransmit movement from the armature to any movable contact spring of asaid associated contact spring group, said armature being disposedthrough said coil with an airgap between the inner walls of the coil andat least one side of said armature, said armature being pivotablymovable in said coil transversally to the longitudinal axis thereof; andsaid stationary loop part being fixed relatively to said coil andadapted to substantially close the magnetic circuit at one single sideof said coil.
 2. An electromagnetic device comprising: a stationarymagnetic circuit part; a magnetizing coil and a movable armature,characterized by the fact, that the stationary part is located whollyoutside said coil and extends parallel to the axis of the coil from oneend of the coil to the other, and that said movable armature is locatedinside said coil and being pivoted at one end adjacent to an end of saidfixed stationary part at one end of said coil; space within said coilenabling pivotal shift of said armature; and the other end of saidarmature disposed outside the other end of said coil and forming aworking airgap with said stationary part.
 3. An electromagnetic deviceaccording to claim 2, characterized by the fact, that said stationarypart is parallel to the coil axis and located only at one side of saidcoil and that said armature is disposed so its said other end shifts toand from said stationary part and by such movement the size of theworking airgap is decreased and increased respectively.
 4. Anelectromagnetic relay device according to claim 2, characterized by thefact that a coil bobbin is provided; at one side of said armature a leafspring is disposed within said coil, said spring having a free end whichabuts against the inside wall surface of said coil bobbin and keeps saidmovable armature in such a position that a working airgap is situatedbetween said armature and said stationary part; said spring structurallycooperating with said movable armature and said bobbin to maintain saidarmature in a predetermined longitudinal position in relation to saidstationary part.
 5. An electromagnetic relay according to claim 4,characterized by the fact, that said leaf spring at the free end thereofis broader than said armature and fits snug within said bobbin so thatsaid leaf spring centers said armature inside the opening of said coil.6. An electromagnetic relay according to claim 4, characterized by thefact that said leaf spring is provided with an aperture, a strip ofnonmetallic sheet material is inserted through said aperture, one end ofsaid strip extending to the airgap and forming a nonmetallic pole-sheet,for preventing the pole surfaces from making direct contact with eachother.
 7. A relay According to claim 6, characterized by the fact thatsaid aperture in said leaf spring is elliptic and that said strip has aportion of reduced width adapted upon assembly to be located in saidaperture for fixing said strip in a predetermined, longitudinalposition.
 8. An electromagnetic device according to claim 2,characterized by the fact, that the cross-sectional areas of said fixedcore part and said movable armature have such dimensions that there willbe magnetic saturation simultaneously in said core parts when normalactuation current is passed through said coil that by such actuation anormal heating of said coil will occur within usual safety margins. 9.An electromagnetic device according to claim 3, characterized by a coilbobbin, and the fact, that said stationary part is U-shaped, with thelegs thereof bent towards said movable armature, that cooperating lugaperture means on a leg of said stationary part and said bobbininterlock said stationary core part to said coil bobbin.
 10. A relayaccording to claim 1, comprising a coil bobbin for the magnetizing coilhaving a flange provided with an extension at one side, said extensionenabling support for one end of contact springs belonging to saidcontact spring group.
 11. A relay according to claim 10, characterizedby the fact, that said extension has apertures therethrough, and circuitconnection ends of said contact springs penetrate through said extensionapertures.
 12. A relay according to claim 1, wherein the contact springgroups are characterized by the fact, that at least one contact set ofthe contact springs is located in an aperture in said actuating rib. 13.An electromagnetic relay according to claim 1, comprising a cover forsaid relay, characterized by the fact, that said cover is provided withat least one opening in which a dust filter is inserted.
 14. A relayaccording to claim 13, characterized by the fact, that said dust filtercomprises a porous washer located at the rear part of said relay, remotefrom the relay contacts, and that said filter is provided with openingsinto which the external connection parts of the springs are tightlyfitted.
 15. A relay according to claim 13, characterized by the fact,that said cover is provided by at least one aperture in the vicinity ofthe contacts, in which a dust filter is inserted.
 16. A relay accordingto claim 1, said relay comprising: at least one changeover contact,characterized by the fact that said changeover contact comprises onemovable contact spring and one fixed contact spring and that said fixedcontact spring is considerably stiffer, by at least approximately tentimes, than the movable spring, and that the contact means of saidmovable contact spring rests against the contact means of said fixedspring so that a breaking contact is obtained, and that said changeovercontact further comprises a second fixed contact spring and a supportingspring, the supporting spring supporting said second fixed spring andbeing at least about ten times stiffer than said second fixed contactspring thus providing the make function of the changeover contact, andfinally that the supporting surface by which said supporting springsupports said second fixed contact spring and also the surface of thatpart of the actuating rib which actuates the movable contact spring arelocated immediately adjacent to the contacts of said springs.
 17. Arelay according to claim 16, characterized by the fact, that said fixedspring for the break function and said fixed spring for the makefunction are double bent to have the shape of a ''''z'''' in thevicinity of the contacts thereof, towards the associated movable contactsprings, so that the height of the solid contacts of said springs isconsiderably less than the thickness of insulating spacing washerslocated between said contact springs.
 18. An electromagnetic devicecomprising: a stationary magnetic circuit part; a magnetizing coil and amovable armature; said stationary part being disposed outside said coiland extending parallel to the axis of said coil from one end of saidcoil to the other end of said coil; said movable armature being disposedinside said coil; means pivoting said movable armature at one endadjacent to an end of said fixed stationary part at one end of saidcoil, the space within said coil enabling pivotal shift of saidarmature; and the other end of said armature being disposed outside theother end of said coil and forming a working airgap with said stationarypart; the cross section area of said armature divided by the area A ofthe space between the armature and the stationary part, available forthe cross section of the winding of said coil, is greater than 0.1 andthat the thickness of said armature divided by its width is greater than0.2.
 19. An electromagnetic device as defined in claim 18, wherein thethickness T of the armature divided by its width B is greater than 0.35and preferably between 0.35 and 0.5.
 20. An electromagnetic device asdefined in claim 18, wherein the cross section area of the armaturedivided by the area A of the space between the armature and thestationary part, available for cross section of the winding of saidcoil, is greater than 0.2 and preferably between 0.2 and 1.0.
 21. Anelectromagnetic device as defined in claim 20, wherein the thickness Tof the armature divided by its width B is greater than 0.35 andpreferably between 0.35 and 0.5.